1. Field of the Invention
The present invention relates to a gas rate sensor for detecting an angular velocity acting in the horizontal direction (in the direction of yaw) and more particularly, to a gas rate sensor which responds neither to gravitational acceleration corresponding to inclination in the direction of roll nor to unwanted acceleration acting in the direction of yaw.
2. Description of the Related Art
In the gas rate sensor disclosed in Japanese Patent Laid-Open No. 29858/1991, heat wires (heat-sensitive resistive elements), a gas passage, a nozzle, and other components are photoengraved in semiconductor substrates by semiconductor fabrication techniques. A gas flow is created by a piezoelectric pump composed of a piezoelectric device. Variations in the resistance values of the heat wires are detected by utilizing deflection of the gas flow striking the heat wires (heat-sensitive resistive elements), and the angular velocity acting on the gas rate sensor in the horizontal direction (in the direction of yaw) is detected.
Since the prior art gas rate sensor makes use of photoengraving techniques of semiconductor fabrication processes, the gas rate sensor can be made small in size. Also, the heat-sensitive characteristics differ only slightly between the heat wires. Hence, this kind of gas rate sensor is adapted for mass production. In addition, the gas rate sensor is excellent in ability to detect angular velocities. However, in the prior art gas rate sensor, the heat wires are spaced closely from each other to make the sensor small, utilizing photoengraving of semiconductor fabrication techniques. Therefore, the sensitivity with which temperature is detected decreases.
In the prior art gas rate sensor, a pressurized heavy gas is sealed in the sensor to prevent the sensitivity from deteriorating. Also, a large temperature distribution gradient is created between the heat wires. In this way, the sensitivity is improved.
In the prior art gas rate sensor, where the pressurized heavy gas is used as described above, unwanted gravitational acceleration corresponding to inclination in the direction of roll and even acceleration acting in the direction of yaw are detected, in addition to the required detection of angular velocity in the horizontal direction (in the direction of yaw).
Especially, where the gas rate sensor is installed on a vehicle and rotates while tilting, the output from the prior art gas rate sensor is the resultant of (1) angular velocity in the direction of gyration, (2) gravitational acceleration (G) corresponding to inclination, and (3) acceleration in the horizontal direction (in the direction of yaw). Consequently, the angular velocity cannot be detected precisely.